Directional antenna system



Feb. 12, 1946. P. H. KREAGER' 2,394,787

DIRECTIONAL ANTENNA SYSTEM Filed Dec. 12, 1941 2 Sheets-Sheet 1 Fig.1

INVENTO'R.

PAUL H. KREAGER 39 2 Q. 33 i ATTORNEY.

Feb. 12, 1946.

P. H. KREAGER DIRECTIONAL ANTENNA SYSTEM F-i'IeiDec. 12, 1941 2Sheets-Sheet 2 INVENTOR. PAUL H. KREA GER ATTORNEY. 7

Patented Feb. 12, 1946 UNITED STATES PATENT OFFICE DIRECTIONAL ANTENNASYSTEM Paul H. Kreager,- Towson, Md... assignor; to Bendix AviationCorporation, South Bend, .Ind., a corporation of Delaware ApplicationDecembe'rlZ, 1941:, Serial .No; 422,627

4 Claims.

ing equipmentaresituated in a position affording maximum convenienceforthe operator. To accommodate varying; installation requirements.remote control of the loop rotation and bearing indication are generallyaccomplished in some' manner permitting the use of flexible'conne'ctlonsfor the transfer of power. Twocommonly usedsystems are a mechanical oneemploying" flex ible shafting, and an electrical one employing anelectric loop drivemotor' and a self-synchronous electric bearingtransmitter at the loop.

An important deficiency of remote control and indication systems is thata failurein the sys tem for remotely indicating the loop position withrespect to the longitudinal axis of theship leaves the operator with nomeans of obtaining radio bearings, ashe is'without definite knowledge ofthe position ofth direction findingloop.

In the use of radio direction finding equipment;

it has been found that the apparent bearing of a transmitter and itstrue bearing often" differ widely, depending on the position of'the shipwith respect to the direction ofarrival-of the electromagnetic energy.Because of the form of the curve of this error as plotted against thetrue bearing, it is usually termed quadrantal error. The presentdomestic procedure is to correct bearings either by consulting a tableof corrections for use with the particular ship, or to accomplish thesame result by incorporating a mechanical compensator in the apparatusfor re peating the loop bearings at the controlpoint.

Because of the speed with which events happen in aircraft navigation,the-popularity. of the-correction tableis rapidly dwindling and itis: be

ing superseded by the latter method. The ac curacy obtainable with themechanical compensator is dependent on the range of corrections to beaccommodated. Bearing errors of the order of 25 degrees ar frequentlyencountered in allmetal aircraft, thus a total'range of adjustment of at1east50 degrees is required in the-compensator. Reduction in the range:of corrections tobe applied bythemechanicai compensatonwhich isaccomplished as a part of my invention, results"- in materiallyincreased accuracy of-the correctedbearings delivered to the operator.

One of the principalobje'cts of my invention is to provide radiodirection finding equipment having'an increased-factor of safetyandgreaterbea'r ing accuracy.

Another object of 'myinvention is to provide:

combinedmeans for the reduction of quadrantal error and for-emergencydirection finding.

Other objects" and advantages will. in part be: disclosed and in part beobvious when the fob-- lowingspecification is read in conjunction: withthe drawings in which:

Figure 1:. is asch'ematic' diagram showing one embodiment-orthe-invention, and Figure 2 is a:

Referringf now in greaterdetailto Figure 1,

the center-tapped-loop winding 1 islocated within the metallic Shield 2having the insulated gap 3- This assembly is securely fittedto-the shaft4,.which-is made of-insulating material and to-" gether they constitutewhat is: generally known as an electro-statically. shielded loop. Theslip ring 5*isdirectly connected to the center tap oftheloop I and tothe shield 2. Aground connection from the slip ring 5 to the base 8' isestablished'throughth -brush 5a. All the loop drive,. bearing.transmission and circuit switching equipment is locatedwithin this-base8 which is mountedon the aircraft skin 9. The lower slip rings 6,- l aremechanically attached to the shaft Land they are electrically connectedrespectively to the two ends of theloop winding l. Aflixed to the shaft4 is the loop drive gear H], which is engaged by the-drive pinion ll ofthereversible electricmotor l2 This-motor- I2 is connected to thereversing. switch- 13in thereceiver I4- by the conducting leads- I5containing. the batteryl6-- as a'sourceof power for the motor.Actuationoi the reversing switch I3 causes the loopassembly tolie-driven in the desired direction. As-the switch: l3 released, thecenter member returns to the neutral position, breaking all powersupplycircults tothedrivingmotor l2, stopping the loop at- -the ch'osenposition.

The self-synchronous bearing. transmitter ll, which may be ofthetype-knowntothe trade as an Autosyn'," is controlled by an extension ofthe shaft 4. The bearing transmitter ii is connected to the remotelylocated bearing indicator E8 of the same type by the connecting cable19. Power for the system is derived from the alternator 20 through theconductors 2 I.

Mounted on the base 8, and enclosing the rotatable loop assembly thereis shown the streamlined housing 22, whose main function is thereduction of the head resistance of the completed assembly. This housingis preferably constructed of some suitable dielectric material.

All of the above parts are already known in combination, and togetherthey form a well 3i of the receiver 14. The fixed loop is now no longera correcting loop, but serves as an emergency loop Whose position withreference to the longitudinal axis of the ship is known. Radio bearingsmay now be taken by the operator through the simple expedient ofswinging the aircraft to the position of null reception and recordingthe magnetic heading of the ship with the necessary correcting angle.

In Figure 2 there is shown an alternative form of the invention in whichprovision has been made for the reduction of vertical pick-up in thefixed loop winding 23 and for improved emergency loopreception duringperiods of precipitation static. A further advantage of this{modification lies in the fact that any number cured, by adhesive orother suitable means, a]

fixed 100p winding 23 which may, depending on the shape of correctioncurve desired, lie in a plane including the axis of rotation of theassembly including loop winding i. Winding 23 may also, be center tappedas shown, with the center tap grounded to the base 8.

In the base 8 there is additionally located the relay 24 having contactassemblies 25, 26, 21. The operating winding of this relayis seriallyconnected. with the switch 28 and the battery 29. by the'leads 30. Therelay 24 is shown in the de-energized position. The armatures 25, 26,,

the rotatable loop winding I is connected'to the.

receiver input circuit 3| through thefront contacts 25, 26 of relay 24and the brushes 611, la, engaging the slip rings 6 and 5, while at thesame time the contacts 21 short-circuit'the fixed loop winding 23. Inthe de-energized position of relay 24, the rotatable loop winding isdisconnected from the receiver input circuit and the shortcircuit isremoved'from the fixed loop winding 23-. The fixed loop winding 23 isnow connectedto l the receiver input circuit 34 through the backcontacts 25, 26 of relay 24 and the adjustable-trimming inductances 34,35 which are set to the desired.- value by means of the movable ironcore 36.

'In-;operating' under normal conditions the switch 28 is closed, therebyoperatingrelay 24 and connecting the rotatable loop winding I tothereceiver M in the normal manner. At the sametime the fixed loopwinding 23 is short-' circuited and thus serves as a correcting loopintroducing quadrantal error of such sign and magnitude as to reduce theoverall quadrantal error of the complete installation on the aircraft.The loop may be rotated to a null posi- 7 tion by operation of theswitch 13 and the bearings read on the bearing indicator l8 in taking aradio fix. However, should a failure occur in the bearing indicatingcircuits, such as the 'burnout of alternator or a break in theconnecting cables, the operator will be without knowledge of the angularposition of the rotatable loop, and consequently cannot take radiobearings.

In an installation incorporatingmy invention,

The fixed loop it is merely necessary that the operator open.

the switch 28, de-energizing relay 24 -and conmeeting the fixedloop'circuit to the input circuit tacts 21 on relay v24. With thisarrangement and the relay 24 in the energized position, the shield,rather than the fixed loop winding 23 itself, is shirt-circuited andthereby acts as the correcting loop. Metallic shielding. 31 preferablyof a type easily formed to fit the interior of the housing 22 such as,for example, the widely used tinned copper loom. The shield may begrounded to the base 8 by a lead as shown.

The trimming inductances 34,- 35rshown in'Figure 1 areincluded to permitadjustment of the electrical characteristics of the fixed loop circuitto present the same loading to the input circuit of the receiver as therotatable loop winding. Suitable design of the fixed loop winding willpermit the elimination of these inductances, but their retention mayprove desirable to permit correction of the normal inductance variationsoccurring during manufacture- I r It is well known that the'formofthequadrantal error. curve depends on the circumstances of aninstallationithe quadrantaler'ror' curves of large steamships1difierin'g'radically from. those of aircraft; While I have shown thefixed loop designed for mounting along the fore and aft axis of a craft,it is neither my intention nor desire to confine myself to thisarrangement, for the fixed loop may have any conceivable orientationwith respect to the zero degree azimuth position .of the rotatable loop,depending on thejshape of the correction curve desired. In installationswhere the housing 22 is not desired, the fixed loop winding and itsshield may be made self-support ing. In securing the necessary operatingcharacteristics, it maybe possible to use a distributed winding for thefixedloop, or even to employ a number of interconnected tofulfillitsfunctions. H r V 7 I 7 H It will be evident that many changesand mod ificati'ons may be made in' the invention without departingfrom'the spirit thereofas expressed in the foregoing description and inthe ap nd ed'claims. a l i Whatiiclaim is:"' p

1. The combination of a radio receiver, a directional antenna rotatablymounted on a'bodv, a'loop antenna fixed with respect to 'said body andlocatedwithin an electrostatic shielding structure having an'insulate'd'gap, said shielding.

structure being 'sodisposed as to. alter the appare plane windingsections ent direction of arrival of electromagnetic energy at saiddirectional antenna when said insulated gap is short circuited, meansfor selectively short circuiting said insulated gap, and switching meansfor alternatively connecting said directional antenna or said fixed loopto the input circuit of said radio receiver.

2. The combination of a radio receiver, a directional antenna rotatablymounted on a body, a loop antenna fixed with respect to said body andlocated within an electro-static shielding structure having an insulatedgap, said shielding structure being so disposed as to alter the apparentdirection of arrival of electromagnetic energy at said directionalantenna when said insulated gap is short circuited, means forselectively short circuiting said insulated gap, switching means foralternatively connecting said directional antenna or said fixed loop tothe input circuit of said radio receiver, and means for adjusting theelectrical characteristics of the fixed loop circuit to match those ofsaid directional antenna.

3. The combination of a radio receiver, a directional antenna rotatablymounted on a body, a loop antenna fixed with respect to said body andlocated within an electrostatic shielding structure having an insulatedgap, said shielding structure being so disposed as to alter the apparentdirection of arrival of electromagnetic energy at said directionalantenna when said insulated gap is short circuited, andelectromagnetically operated switching means for selectively shortcircuiting said insulated gap and for alternatively connecting saiddirectional antenna or said fixed loop to the input circuit of saidradio receiver.

4. The combination of a radio receiver, a directional antenna rotatablymounted on a body, a loop antenna fixed with respect to said body andlocated within an electrostatic shielding structure having an insulatedgap, said shielding structure being so disposed as to alter the apparentdirection of arrival of electromagnetic energy at said directionalantenna when said insulated gap is short circuited, andelectromagnetically operated switching means for selectively shortcircuiting said insulated gap and for alternatively connecting saiddirectional antenna or said fixed loop to the input circuit of saidradio receiver, said gap being short circuited when said directionalantenna is connected to the input circuit of said radio receiver, theshort circuit being removed when said fixed loop is connected to theinput circuit of said radio receiver.

PAUL H. KREAGER.

